The present invention relates generally to a coupler for wireless communications, and more particularly to the use of a novel air-core or dielectric core coupler as a matching device to the characteristic impedance of the air for a transmitter and receiver for wireless communications.
A well-known problem in wireless communications concerns the effects of reflections of a transmitted signal off of the walls of buildings, people, etc. on the transmitted signal as in propagates through the air. These reflected signals cause notches that come and go in the bandwidth where communication takes place, thus degrading transmitted signals. Any such degradation of transmitted signals in wireless communications are extremely costly because it will limit the usage of bandwidth which will result in slower communication speeds and in certain areas the communication devices will not work or will work poorly.
Most of the work to find solutions to the problems of signal losses due to reflected signals has focused on digital signal processing techniques such as Spread Spectrum and CDMA. In Spread spectrum techniques, the bandwidth of a transmitted signal is spread over a large range of bandwidth to communicate the same information in several frequencies. This way, notches in the communications bandwidth will not stop communication to everywhere. The drawback with this technology is that the need to use a wide bandwidth and the interference that is generated from the transmitter and from reflections can result in a complete inability to communicate.
The CDMA technology uses a single carrier frequency and is capable of detecting reflected signals in delayed time sequence. In theory, this should work fine, but, in reality, very fast sampling is required as well as the ability to detect very weak signals. This means a very high price today for effective communications. Also, due to non-real-time communication detection, this technology is probably limited to a couple of MBps transmission speed.
Moreover, regardless of the utility of techniques such as CDMA, reflected signals will still cause notches in the communications band of interest as a result of the basic physics that limits the antenna as a matching device for transmitters and receivers. The characteristic impedance change in the air from walls and other objects reflects back to the transmitter and receiver, which causes notches in the communications bandwidth. The two impedances (air and transmitter/receiver) need to be matched to each other to avoid notches in the communications bandwidth.
There is thus a need for a coupler that is capable of matching the impedance of the air with the impedance of a wireless transmitter and receiver in order to eliminate notches in the communications bandwidth.
Briefly stated, in a first embodiment, the present invention is a communications apparatus for transmitting electric or electromagnetic signals over air having a characteristic impedance. The communications apparatus comprises:
a transmitter having an output impedance, the transmitter for transmitting the electric or electromagnetic signals at a preselected frequency; and
a coupler connected to the transmitter, the coupler comprising a transformer having a non-magnetic core, the transformer communicating the electric or electromagnetic signals to the air, the coupler matching the output impedance of the transmitter to the characteristic impedance of the air.
In a second embodiment, the present invention is a communications apparatus for receiving electric or electromagnetic signals from air having a characteristic impedance. The communications apparatus comprises:
a receiver having an input impedance, the receiver for receiving the electric or electromagnetic signals at a preselected frequency; and
a coupler connected to the receiver, the coupler comprising a transformer having a non-magnetic core, the transformer receiving the electric or electromagnetic signals from the air, the coupler matching the input impedance of the receiver to the characteristic impedance of the air.